The use of cylinder charge swirl in internal combustion engines to promote fast and efficient combustion, especially at part load, is well known. Numerous methods for obtaining inlet charge swirl have been devised, including variously shaped intake ports and stationary flow guides or vanes. Such fixed geometry arrangements, in general, provide less than ideal results, in that the amount of swirl obtained in part load or part throttle conditions is less than desired or the swirl devices impose an undesirable restriction to inlet flow under full load or full throttle conditions.
Some attempts have been made to provide variable port geometry to obtain the desired combination of high part throttle swirl with low restriction at full throttle or maximum load. Such arrangements generally have involved devices located at the intake port entrance or in the runner substantially upstream from the end portion of the port adjacent to the cylinder and distal from the head of the associated intake valve.